Electric accumulator



April 29, 1952 H. G. ANDRE ELECTRIC ACCUMULATOR Filed Nov. 27, 1950 w ni w lk m yf lo o r\ Q l N 0J l CL g (3 O a i II 2 lNVENTOR z: HEN G.ANDRE lg 73m AGE NT Patented Apr. 29, 1952 signorto Yardney'i.International Gorp.,v Newl York, N. Y., av corporation of. New` York`ApplicationNovembe1'27, 1950, Serial No'.

res-nso'.

InFranceNbvemlier 29,1 1949i (o1. 13a-e.)

1V inventionrelates to a. batterykv of" theltype disclosed i'nmy'cci-pending U. S. Application. Ser; No'i $381,702; filed April-1 1947-.Inisuchab'attery, or' reversible;electro-chemical energy generator,- oraccumulator; the ionicexclianges between the'.

electro-chemically activejsubstances are eiected. through asemi-permeable material'` which serves as a separator member'- andT isimpregnated. with electrolyte:

The invention its* more; particularly-Y directed.' to suchaccumul'atorsY wherein'` the electro-cliemi-l callyf activematerials ofopposite-polarity: are; ap-A plied under pressure against4 tl-'ieoppositev sides.

of sucr'r a semi-permea'lfiley separator or diaphragm member;

The procedureV of applying' electro-chemicallyactive' materia-ls` underpressure aga-inst'- a diaphragm has constituted a decisiveadvanceintleart of reversible electro-chemical energyegenerators; It hasmadeitpossille' to limit theamount ofelectricity'present' in anaccumulator, and-to f'ul'll' its4 operative function; in retentionwithin-f a solidiv material v rather than: in tle` liquid state; which;aside from obvious facilitation of handlingl and' manipulation', hascompletely altered? the very character of"tlieelectro-cllemicalreactions involved;

However; the, constructionl ofy such accumula.- tors liras until new'raised; certain d'ii'culti'es. Thus, takingy the instance! ofa-naccumulator Whereintli'e electro-chemically active substances aresilver;4 anclzincv and the semi-permeakle material' is the` regeneratedcellulose sheet'V material known as' cellophane, whereas suoli anaccumula .tor i'sea'sy enough-.to makein the'l'aboratory'undertheiguidance oa skilled expert andwhen resort-- ingt'ofall thel usualprecautions taken in the cone struction of a prototypemodel, tle*resultsare foundM to loe-much less uniform where the pro-4 duction isentrusted to workers, however'skill'e'd',

who cannot be expected t'o'- display the same amount ci care astl'ieengineer or scientist.. if onlyffor..y considerations offoutput.

It. has been sought forsome timetofascert'ain the; causesfo such lack ofuniformityiandtexf plain why, While some'V off the accumulators pro`duced do possess theY characteristics expectedi off them, ai number ofspecimens" were ordinarily producedA in which either the capacitywastoolowv or the useful life tooV short; even though no diierences instructure could be detected' as compared to the'satsfactoryunits.

Whileit had beenV seen that the successi-utoperation of theaccumulatordepended ontl'i'e pres"- sure' prevailing'in it betweenV theactvematerials 2 andy the diaphragms.. it wasbelieved; that this pressure;could: be allowed to.` vary over quite a.

wide range: without,4 producingf any critical modify lcations in. the.Acharacteristics of, the; unitiv As.' the: said. pressure results. from;al swelling ofv the semi-permeable. materialowing; toits; impregna.

tion.y by. electrolyte... itl wasV endeavored to;.optain.. a:satisfactory operative pressure byf suitably se.-v

lectng,. an. approximate:ina-nner,Y thejthickness( orf depth of thesemi-permeable member. in. its. dry' state relativelyj to. thetclearance reserved: for.' it in the tank by the active materalspsuchl.that.. after swelling, the resulting. pressure.:` would; approximatethatfwhich was; bvelijevedvto prevailin apreviously: constructedaccumulator whichrhaddisplayedlgoudresults.

Such. ani empirical procedure, inV additicnl to'. the irregular: results'.to whicnit isf conductive.; as"- mentionedhereabove;.provides no meansof trans,=

ferri'ng. pro duction` from' onei type: of; accumulator,`

tof4 another type; dii'eringf from the; rst. in; ejlec trical powervcapacitm. orxby itsaloility for rapid',-

discharge, etc. It; is anoljectofrthis;invention tomelet.thisvinadequacyoithe prior'art. It isaanlobjgec't toprovide'.anaccumulatoriof the type;specified.wherein` tliey electro-chemicallyactive substances are aplpliedl under: pressure afgainstgoppositesidesor a semiepermealole"v member.;`v may be.l expected.. with.vpos-itix/'eAv certainty. to.-- yieldcptimum; results,-

regardless.l of: its: capacity.. Another; object isto.A4

providaia, meansof; selectingfv auw-ill... from; among. the various.known lorrnsv ofelectroneconstruee;

tion.. that? particularformY which; will lend; itself.

to easy' construction while; leading toithe.: .'iesiredlresult,.witlioutanydangei' ofsuch selection-.being adversely` rene'cte'din. characteristics; of; the? apparatus, contrarlly to; what almostinevitably' occurred-heretoforel.`

Systematic testsliave been conducted-. to` as@ certain' tlieA`conditions to be fulfilled infordeiv t@ olitan' withcertaintysuccessiur'operation`v an l accumulator" oiY t'liej specie'd type. Flor1this? pur={A pose., it has beensou'glit to definethe-structuralcharacteristics to` be imparted to tlie` electrodes and', morespecifically, ti'ie relativetliicltness or. depth dimensions, to. 'belimparted to. tle acltye 'substancesJ and; diaphragms'in or'c l`er`to-seciirep. within. the.iin-ishod` accumulator-,- apredeterniined Jvalue-of-thepressure underrwhich.tnegactivesuhstances are applied1against: theqopposite sides; ot.

saiddiaphragms; Y

Irrthe.accompanyingtdifawing: Y Eig; 11 illustrateaatestingfdevice-.whiclnisgusefulf 3 in the construction of a battery according tothe invention;

Fig. 2 is a pressure diagram obtained with the device of Fig. l;

Figs. 3 and 4 are further diagrams illustrating importantcharacteristics of a battery according to the invention; and

Fig. 5 is a fragmentary section through a battery representing anembodiment of the invention, enough being shown of the battery toillustrate the relative arrangement of its component parts.

An accumulator of the type specified comprises a multiplicity of layersor laminae of positive substance alternating with a multiplicity oflayers or laminae of negative substances, each pair of adjacent layersor laminae of opposite polarity being separated by a diaphragm and theentire laminated assembly being disposed in a container.

Let l be the distance between the parallel sides of the containerextending in a direction parallel with the layers of active substancesand the diaphragms, and e the combined thickness of the layers of activesubstances in the dry state; then the said pressure which prevails afterthe electrolyte has been added depends on the ratio c of the difference(Z-e) or clearance i, left free in the container by the activesubstances for receiving the diaphragms, to the sum total of thethickness dimensions d of said diaphragms in the dry state.

The curve representing the variations of said pressure AP versus thoseof the ratio a has been plotted. For this purpose, the devicediagrammatically illustrated in Fig. 1 has been designed. This apparatusessentially consists of a boxshaped container i two of the side walls ofwhich are shown at I I and I2 and the bottom at I3. The walls and thebottom have sucient rigidity such that they may be regarded asundeformable under the operating pressures developed.

Secured to the upper surfaces of said side walls II and I2 is a crossmember I4 formed in its center with a hole I for guiding a piston rod I6having rigidly secured to its lower end a piston Il substantiallyrectangular in horizontal cross section, and adapted for slidingmovement in the container I0, suii'icient clearance being provided inthe sliding fit of the piston in the container for allowing substance,especially liquid, to pass from one to the other of the two chambers orcompartments I8 and I9 defined by the piston in the container.Upstanding on the container is a structure 2B including two uprights 2Iand 22 and an upper cross-bar 23 which supports at its center apreferably threaded rod 24 cooperating with a complementary hole formedin the cross-bar 23. The rod 24 carries at its base a small plate 25which serves as an abutment for a -compression coil spring 26 ofcalibrated resiliency, and abutting at its lower end against a plate 21rigid with the piston rod I6. The plate 21 supports a pointer 28 adaptedto cooperate with a scale of calibrations 29 supported from the crossbar23.

A laminated pile of cellophane sheet elements, in the dry state, ofmeasured thickness in the uncompressed condition, is inserted into thecontainer I0 under the piston I1. The said thickness or depth of thepile in uncompressed condition, referred to as d, may, indeed, bemeasured in the apparatus itself, by reading first the position of thepointer 28 when the piston I1 rests on the bottom I3 of the container,and then its new position with the piston resting on the top of the pileof laminated sheets substantially under zero pressure. Starting fromthis condition, the piston i1 is raised by a vertical distance i, thisdistance being ascertained by means of the pointer 28 cooperating withthe calibrated scale 29. The vertical position of the plate 25 is thenso adjusted that, for this position, the compression of the spring isnil, while as soon as the plate is raised above this position the springwill be subjected to compression.

The swellingly acting electrolyte, e. g. a water solution of potassiumhydroxide, is then introduced into the compartment I9 by the simpleprocedure of pouring it onto the piston I1 whence it flows into thelower compartment through the clearance intentionally provided betweenthe sides of the piston and the walls of the container I0.

The cellophane sheet elements contained in the compartment I9 swell; thestack increases in thickness until it reaches up to the under face ofthe piston I'I, and thereafter, on further swelling, pushes up thepiston against the action of the spring 26 which contracts. The sag ofthe spring may be indicated by the displacement of the pointer 2 overthe scale 29; this reading yields, with due allowance for the initialadjustment, an indication of the pressure P. The curve of variation ofthis pressure as a function of the above-defined factor a may thus beplotted. A typical such curve has been shown at A in Fig. 2, wherein thevalues of the factor a are plotted in abscissae and the pressures P(expressed in kg./sq. dm.) in ordinates. It can be ascertained from thiscurve that the pressure increases as` the fourth power of the factor a.

This surprising discovery explains the irregu` lar results obtained inthe past in the construction of such accumulators, in that it shows thata very small difference in the thickness of the diaphragms relatively tothe total clearance, providedfor them in the container by the activesubstances, can entail very considerable differences in the operatingpressures.

Thus, in this connection, the invention is based upon the discovery ofthe critical character of said diaphragm thickness, and of the need forselecting such thickness with the utmost care and accuracy. From this itcan be inferred that an essential specication in the manufacture ofaccumulators designed for operation in the man.-

ner described lies in the number of sheets of regenerated cellulose orcellophane (since their individual thickness is, in practice, verynearly constant) which are to be interposed, .whether rolled or packedaround or otherwise, between the active substances of opposite polarityin the accumulator. Y

Actually the pressure under which the active substances of oppositepolarity are applied against the diaphragms within the accumulator isnot, strictly speaking, the pressure defined by the above-describedcurve A as a function of the factor a; thus, allowance must be made,inthe first place, for the contraction or shrinkage of the activesubstances which occurs in the course of operation of the accumulator,and, moreover, for the slight distortion assumed by the container underthe action of the forces developed against its opposite walls. Thecompression curves which make allowance for both these factors have alsobeen plotted.

To take into account the compression of the acti-ve substances,completey accumulatori have-been dismantled, which present structuralLAy measured; and it; was found-thatai certain degreci ofvv contractionhasv occurred.. therein rela-1 tively to the thickness. of sai-delectrodesin. the: drystate.v

The; corrected compression curve which maires: allowance forthis-contraction is shown atHB in Fig. 2', andity is seen. that: itsygeneral" shape. is: exactly.' similar tothat of the-curve-fr, and; that:it. can-be-:regarded'as being the curveA merely shifted a directionparallel to: the. axisy of. abscissae. shows that, in. the instanceunder` investigation, the f contraction of. the active substancesamounts to about'. 10%..

Lastly, the corrected curve. which, in*` addition to theicontractionofthe activev substances, at the same time takes into account the slightexpansion of the container is shownv as the curve lC, whichmay also beseen as resulting from the curves A and'B by a translation parallel, tothe axis of abscissae.

This cur-ve C. provides the. manufacturer' with accuratedata on thethickness which is to be imparted to the semi-permeable.` substancetaken inpthedryA state, or, in practica, the numberof sheets ofcellophane to be used for. each electrode, in; order toobtain, in theoperation of thefaccumulator under construction, a predetermined valuefor the pressure of application of said active substances against thecellophane separators.

It is found, by way of example, that in order to obtain a normaloperating pressure of 2O kg./sq. dm. the combined cellophane thicknessshould be selected such that the factor a should be slightly higher than2.30. This information is especially valuable in view of theexperimental results, indicated hereafter, provided by very numeroustests carried out with the object of ascertaining the most favorableinternal pressure for optimum operation of an accumulator.

With the above teachings in mind, accumulator units have beenconstructed diiering from one another in their internal operatingpressure, that is the pressure of application of the active substancesagainst the separator diaphragme. Then the electric capacities of eachof these units was plotted as a function of the said pressure, forvarious rates of discharges. Curves were thus obtained such as shown atD, E, F on the diagram of Fig. 3, wherein the pressures in lig/sq. dm.are plotted in abscissae and the capacities in amp. hrs. in ordinates.

The curve D was found for complete discharges of the units in .twohours, the curve E .for complete discharges of the units in ten hours,and the curve F for complete discharges in 24 hours. These curvesl showthat optimum capacity, in each of the three cases, is for an internalpressure approximating 20 lig/sq. dm., and that this capacity drops ofibut slowly as the pressure is decreased from 20 lig/sq. dm. to 15lig/sq. dm., while it drops on" at a comparatively very fast rate as thepressure is increased above 20 or 2l kg./sq. dm.

Keeping in mind both the curves of Fig. 2 and those of Fig. 3, thereason why accumulator units produced in an apparently quite similarComparison between-1` curves. and; B.-

6 manner.: displayed such. wide differences irrsenviot performancevbecomes obvious; Itis: seeirthatzitj is suicient` for the internal.pressure; tori/tary. only by one. or two: lig/sq. dm. for the; capa@ tobe cut down by 5.0 Now; avariationoij 1401's 2 kg./sq. dm. correspondsvto only a percent.l variation in the: ratiora. In practice,tlsrisinreansv that the insertion of only one or twoy cellophane.sheetsv too many during the. construction org` am; accumulator'is enoughgravely-"to: impairfthezultimate operatingcharacteristicsofttl'reiun-ih` Further experiments have been: conduetedon accumulatorspossessing different; internaligpres? sures: with the, object of'ascertaining theA 'indu-1 ence. ofv such pressure. on servicelife.. Theresults'. of these tests are summarized-in graphicl forni.. in the curveof Fig. e, wherein internalpressure is plotted in abscissae versus: the:numberf ofi the unit's useful operating: cycles in. ordinates-.fiAThe... curve G thus obtained" displaysv a. maximum. a pressureVapproximating 20 lig/sq.. din-.3.; which. the number ofoperatingcycles;attains 400;.. It decays, thoughsl'owly, as.thefpressure.- ist-increased above the said. value; but on. the: other:hand itV fallsA comparatively'rapidly as.: the ternal pressure isreduced' below 20 kg./sq:. dma.

These last-mentioned experiments'vt'hus: dem.-L onstrate: that, Whereit; is: desired; to.k obtain an accumulator having'A a: long-service..lifje,. it'. nec-f essary that. the: pressure bei not; substantiallylower thai/1:20 kgr/sqa. For: reasonssimilarto. those explained aboveYin: thediscussionzoi the: curves' D; E, F, itiisr seent thattlielaclc'oifv only-@nef orl two sheets:` cf; cellophane.L has` a;veryadverse@ eiect. onthe; operation of, anzaccumulator;

Now'V to combine;` the teachings resulting; from:v the consideration ofFigs. 2 to 4, the necessary conclusion is that both the excess and thedenciency of one or two sheets of cellophane result in highlydetrimental consequences on the accumulator performance, and that theprescriptions as to the number of cellophane sheets used to wrap theactive substances sh-ould be scrupulously followed. Such prescriptions,which are Very easy to observe strictly, by a mere eiort of attention,make it possible to provide accumulators which possess all the highqualities expected of them as resulting from the tests conducted on theprototype model. The simplicity of the improvement provided by thisinvention, far from detracting from its importance, confers to it anessential value, inasmuch as it makes it possible to achieveconsiderable improvement in production without increasing the cost ofmanufacture and without requiring any alteration in plant.

Theoretical considerations may lbe put forward to explain the resultsyielded by the practical tests described herein. An excessive pressureapplying the active substances against the diaphragms tends to retard,and finally completely to inhibit, the ion diffusion and exchanges.

On the other hand, in the case the pressure of application is too low,the electrodes are insufficiently constrained, so that the activesubstances. including especially the negative active substance, tend todrop to the bottom of the container.

However that may be, it was impossible to predict the decisiveimportance, from the standpoint of operating performance, of themeasurement of the means for obtaining the internal pressure, and thisexplains the diiculties encountered heretofore and now overcome.

Fig. 5 shows part of a battery according to the invention comprising acasing 2H wherein there are assembled under pressure, as hereinabove setforth, a set of positive electrodes 210 alternating with negativeelectrodes 2I8. The negative electrodes consist essentially, in thedischarged condition of the battery (as disclosed in my above-identiedco-pending application) of zinc oxide, the positive electrodes beingcomposed essentially of silver. An alkaline electrolyte (not shown)permeates the sheet material 22B, here indicated to consistofcellophane, which separates adjacent electrodes from one another.

In the light of the foregoing it will, of course, be apparent that thebattery shown in Fig. 5 is merely an illustrative example and thatdepartures `therefrom are permissible within the spirit and scope of theappended claims.

l. An electric accumulator, which comprises at least one positiveelectrode containing silver, at least one negative electrode containingzinc juxtaposed with said positive electrode, a semipermeable materialbetween said electrodes, an alkaline electrolyte impregnating saidelectrodes and said material and exerting a swelling iniluence on saidmaterial, the swelling of said material applying the same against saidelectrodes under a pressure at least 15 lag/sq. dm.

2. In an electric accumulator, in combination. a casing; a plurality ofelements juxtaposed in said casing including at least one positiveelectrode, at least one negative electrode, a semipermeable material,and means including said material separating electrodes of oppositepolarity; and an electrolyte in said casing permeating said electrodesand said material, said electrolyte having a swelling iniluence uponsaid material,

the ratio of free space, computed as the difference between thedimension of said casing noi-malato said electrodes and the combinedthickness of all of said elements other than said material, to the totalthickness of said material, when in the dry state, being within a rangeof substantially from 2 to 3.

3. In an electric accumulator, in combination, a casing; a plurality ofelements juxtaposed in said casing including at least one positiveelectrode containing silver, at least one negative electrode containingzinc, and a semi-permeable material between adjacent electrodes ofopposite polarity; and an alkaline electrolyte in said casing permeatingsaid electrodes and said material,` said electrolyte having a swellinginfluence upon said material, the ratio of free space, computed. as thediierence between the dimension of said.

HENRI GEORGES ANDRE'.

REFERENCES CITED The following references are of -record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date 1,955,115 Drumm Apr. 17, 19342,317,711 Andre Apr. 27, 1943 2,339,031 Rosenberg Jan. 11, 19442,407,648

Boehm, Jr Sept. 17, 1946

1. AN ELECTRIC ACCUMULATOR, WHICH COMPRISES AT LEAST ONE POSITIVEELECTRODE CONTAINING SILVER, AT LEAST ONE NEGATIVE ELECTRODE CONTAININGZINC JUXTAPOSED WITH SAID POSITIVE ELECTRODE, A SEMIPERMEABLE MATERIALBETWEEN SAID ELECTRODES, AN ALKALINE ELECTROLYTE IMPREGNATING SAIDELECTRODES AND SAID MATERIAL AND EXERTING A SWELLING INFLUENCE ON SAIDMATERIAL, THE SWELLING OF SAID MATERIAL APPLYING THE SAME AGAINST SAIDELECTRODES UNDER A PRESSURE AT LEAST 15 KG./SQ. DM.